The present invention relates to a method for holding and precisely centering an electronic component for the purpose of and prior to the placement of the component on a circuit substrate or the like, and to an apparatus suitable for practicing the method.
It is known to hold an electronic component by using a sucking device which has an air sucking passage open at an end face thereof. Such sucking device is capable of easily retaining and releasing the component, but has no capability of accurately positioning the component by itself. For this reason, it has been a common practice to employ positioning or centering means for correcting the position of the component which has been sucked on the sucking device. An example of such centering devices is disclosed in U.S. PAT. NO. 4,135,630, wherein a spindle housing which supports a sucker spindle longitudinally movably carries a pair of opposed first axis locators and a pair of opposed second axis locators which are pivoted such that the ends (positioning fingers) of the locators are opened and closed along the first and second (X and Y) axes which are perpendicular to each other. The electronic component held under vacuum on the tip of the sucker spindle is centered by the closed ends of the locators by holding the component on four sides thereof in a sandwiched fashion in both first and second directions normal to each other. The opposed positioning fingers at the ends of the locators are adapted to move in symmetrical relation with each other with respect to the centerline of the sucker spindle, and consequently the centering of the component into alignment with the spindle centerline is achieved through the symmetrical or concentric inward movements of the positioning fingers toward the component. Another example is shown in Japanese Patent Application laid open Mar. 30, 1983 under TOKU-KAI-SHO No. 58-53887. In a holding and positioning apparatus disclosed in this Application, a holder body which supports a sucker for longitudinal sliding movement is provided with a single pair of opposed positioning jaws which are pivotable to align a sucked component in one direction. The component is then aligned in another direction perpendicular to said one direction by means of another pair of opposed positioning members disposed on a positioning device which is separate from the sucker assembly. Like the positioning fingers of the opposed locators shown in the above indicated U.S. Patent, the positioning jaws or members are moved in symmetrical relation with each other with respect to the centerline of the sucker, and therefore the component is pushed into alignment with the center of the sucker.
Holding and centering devices as discussed above are capable of holding an electronic component on a sucker in precise alignment with a predetermined reference position. Thus, an accurate positioning of the sucker with respect to, for example, a printed-circuit board (PCB) substrate, will enable the component held on the sucker to be precisely orientated or positioned relative to the substrate and placed at required positions on the substrate with accordingly high accuracy.
However, the holding and centering device of the type discussed suffers a problem which arises from the arrangement that the positioning of the sucked component in the second direction is effected while the component is gripped by the first pair of positioning members (jaws or fingers) which have positioned the component in the first direction normal to the second direction. In other words, the second pair of positioning members are operated to push the gripped component for aligning the component in the second direction. Under this condition, a smooth movement of the component in the second direction by the second pair of positioning members is prevented by a friction force between the component and the first pair of positioning members. Alternatively, an absence of a frictional sliding movement between the component and the first pair of positioning members would result in the component being moved in the second direction together with the first pair of positioning members while the latter are subjected to elastic deformation. Upon release of the second positioning members from the component which has been positioned in the second direction, the component tends to move in the second direction toward its original, unaligned position due to elasticity or spring force of the deformed first positioning members. Thus, the prior holding and centering apparatus is disadvantageous and not completely satisfactory in its positioning or centering accuracy.
It is further recognized that the possible sliding movement of the component in frictional contact with the first pair of positioning members in the second direction will cause the component to be scratched or scored on its sides. As another drawback, the frictional sliding of the component which generally uses ceramic material for its base will also cause easy wearing of the positioning surface of the positioning members and necessitate frequent changes of the worn-out positioning members.